1. Field of the Invention
The invention relates to an apparatus for detecting the position of the paintball of a paintball gun, and more particularly to an electrostatic capacity detection apparatus that is positioned in the firing area. Unlike the conventional infrared transmitting/receiving way to create the reflection or interruption state, the feature of the electrification of the paintball is utilized for detecting the fact if the paintball completely reaches the firing area. In this way, an immediate and accurate detection is ensured.
2. Description of the Related Art
In recent years, paintball gun has become a popular outdoor recreational sport. As shown in FIGS. 1 and 2, a paintball gun includes a paintball-feeding unit 12 at the top of the gun barrel 11. Several paintballs are accommodated within the gun barrel 12. A high-pressure tank 15 is attached to the bottom of the gun handle 13. A firing element will be actuated by the gas released from the high-pressure tank 15 when a trigger is pressed by the finger such that the paintball is discharged.
The gun barrel 12 is filled with several paintballs 20. As shown in FIGS. 3 and 4, the paintball 20 passes through a guide tube 16 and enters into a firing area 17. At that time, the paintball 20 will be detected by sensors 18 at both side of the firing area 17 to determine if it is fed in place. Then, the signal will be transmitted via a lead 19 to a circuit board (not shown) within the gun handle 13 for controlling the firing action.
However, the sensors 18 have to be installed at both side walls of the firing area 17 such that an infrared transmitting/receiving action takes place to determine if the paintball is located in the firing area 17. The sensing way can be divided into reflective and blocking type according to the light path. The reflective type easily causes a false determination due to the color of the paintball 20. For example, the black paintball 20 has a small light-reflective amount such that the detection circuit may make a false determination that no paintball 20 is present since it does not obtain sufficient reflective light. As a result, most of the paintball guns employ the blocking type sensors. However, the blocking type sensors still have the following drawbacks in use:    1. The interference of other light sources: The sun daylight and the artificial light source include a spectrum of infrared, visible light, and ultraviolet. If the other light sources fall on the optical receiver and if the light intensity is so great that the optical receiver does not work due to the light saturation, a false determination may take place since the detection circuit is not properly responsive to the light falling on the optical receiver. Particularly, this often happens to the transparent or translucent paintball-feeding units 12. The other light sources can pass through the paintball-feeding unit 12 and reach the firing area. The light-blocking type paintball detection circuit may make a false determination if the light is strong enough. Originally, it is a good design that the number of the paintballs 20 is visible through the transparent or translucent paintball-feeding units. The user will be disappointed when the light-blocking type paintball detection circuit does not work due to the light disturbance. In addition, the light or paintball detection circuit may also make a false determination when the gun barrel of the paintball gun is directed to the light source and the light enters from the gun barrel directly into the firing area (if the light is strong enough).    2. The light transmitter and receiver are vulnerable to the contamination of the contents of the paintball such that a function failure takes place. The light-blocking type paintball detection circuit must be received within a cavity laterally extended (while the paintball 20 is discharged in longitudinal direction). The light transmitter and receiver are accommodated within the cavity. The light transmitter and receiver are always provided with openings at the detection end thereof. The paint filling of the paintball will fill the openings, thereby blocking the light transmitter and receiver and leading to a function failure when the paintball 20 is unfortunately broken. Even, the paint filling of the paintball will flow along the openings to the circuit behind the light transmitter and receiver. The paint filling of the paintball is conductive so that the light-blocking type paintball detection circuit will be affected. It is probable to lead to a function failure of the light-blocking type paintball detection circuit. The paint filling of the paintball is corrosive. The paintball gun will be damaged when the paint filling flowing along the openings to enter into the paintball gun is not cleaned up in time. However, the paint filling is not easily cleaned up at once due to the shape of the openings. It is not possible to immediately clean it up at the playing field. The paintball is more easily broken when the paintball gun has a malfunctioned paintball detection circuit. The push tube may get stuck by the broken shell of the paintball, thereby causing a problematic discharge. Moreover, the fired paintball may have an instable track in the air when the previously broken paintball leaves the paint filling on the new discharged paintball 20 (even without getting stuck). A light shade may be mounted to resolve the above-mentioned problem. The light travel direction may be unreasonable due to the shape and the angle, thereby considerably reducing the accuracy in determination. Besides, a disturbance by the external light source may occur.    3. The light-blocking type paintball detection circuit of the light transmitter and receiver is employed to detect the lower part of the paintball. The paintball will be sensed when it falls as low as possible. In this way, the paintball may be discharged when fed in place. Otherwise, the paintball 20 may get stuck or broken when fired if it falls only to a half position. Theoretically, the optimal detection point is the lowest point of the paintball. In fact, there are still gaps in the firing area so that the paintball may roll therein. In order to enable the paintball to block the light, the detection point must be raised so that the lowest point can not be detected.
Therefore, the conventional way to detect the paintball requires further improvement.